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<para>
The &t-link-gettext; toolset supports internationalization and localization
of SCons-based projects. Builders provided by &t-link-gettext; automatize
generation and updates of translation files. You can manage translations and
translation templates similarly as it was done with autotools.
</para>
<section>
<title>Prerequisites</title>
<para>
To follow examples provided in this chapter setup your operating system to
support two or more languages. In following examples we use locales
<literal>en_US</literal>, <literal>de_DE</literal>, and
<literal>pl_PL</literal>.
</para>
<para>
Ensure, that you have <ulink url="http://www.gnu.org/software/gettext/manual/gettext.html">GNU gettext
utilities</ulink> installed on your system.
</para>
<para>
To edit translation files you may wish to install <ulink url="http://www.poedit.net/">poedit</ulink> editor.
</para>
</section>
<section>
<title>Simple project</title>
<para>
Let's start with very simple project, the "Hello world" program
for example
<programlisting>
/* hello.c */
#include <stdio.h>
int main(int argc, char* argv[])
{
printf("Hello world\n");
return 0;
}
</programlisting>
Prepare <filename>SConstruct</filename> script to compile the program
as usual.
<programlisting>
# SConstruct
env = Environment()
hello = Program(["hello.c"])
</programlisting>
</para>
<para>
Now we'll convert the project to multi-lingual one. I assume, that you
already have <ulink url="http://www.gnu.org/software/gettext/manual/gettext.html">GNU gettext
utilities</ulink> installed. If not, install them from your preffered
package repository, or download from <ulink url="http://ftp.gnu.org/gnu/gettext/">
http://ftp.gnu.org/gnu/gettext/</ulink>. For the purpose of this example,
you should have following three locales installed on your system
<literal>en_US</literal>, <literal>de_DE</literal> and
<literal>pl_PL</literal>. On debian, for example, you may enable certain
locales through <command>dpkg-reconfigure locales</command>.
</para>
<para>
We first prepare the <filename>hello.c</filename> program, for
internationalization. Change the previous code so it reads as follows:
<programlisting>
/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
bindtextdomain("hello", "locale");
setlocale(LC_ALL, "");
textdomain("hello");
printf(gettext("Hello world\n"));
return 0;
}
</programlisting>
This way we prepared source code. Detailed recipes for such preparation can
be found at <ulink url="http://www.gnu.org/software/gettext/manual/gettext.html#Sources">
http://www.gnu.org/software/gettext/manual/gettext.html#Sources</ulink>.
The <function>gettext("...")</function> in above source has two purposes.
First, it marks messages for <command>xgettext(1)</command> program, which
we will use to extract from the sources the messages for localization.
Second, it calls the <literal>gettext</literal> library internals to
translate the message at runtime.
</para>
<para>
Now we shall instruct SCons how to generate and maintain translation files.
For that, we use &b-link-Translate; builder and &b-link-MOFiles; builder.
First one takes a couple of source files, extracts internationalized
messages from them, creates so-called <literal>POT</literal> file
(translation template), and then creates <literal>PO</literal> translation
files, one for each requested language. Later, during the development
lifecycle, the builder keeps all these files up-to date. The
&b-link-MOFiles; builder compiles the <literal>PO</literal> files to binary
form. After all, we install the <literal>MO</literal> files under directory
called <filename>locale</filename>.
</para>
<para> The complete code of
<filename>SConstruct</filename> script for multi-lingual "Hello world" will
be following:
<programlisting>
# SConstruct
env = Environment( tools = ['default', 'gettext'] )
hello = env.Program(["hello.c"])
env['XGETTEXTFLAGS'] = [
'--package-name=%s' % 'hello',
'--package-version=%s' % '1.0',
]
po = env.Translate(["pl","en", "de"], ["hello.c"], POAUTOINIT = 1)
mo = env.MOFiles(po)
InstallAs(["locale/en/LC_MESSAGES/hello.mo"], ["en.mo"])
InstallAs(["locale/pl/LC_MESSAGES/hello.mo"], ["pl.mo"])
InstallAs(["locale/de/LC_MESSAGES/hello.mo"], ["de.mo"])
</programlisting>
</para>
<para>
Generate translation files with <command>scons po-update</command>.
You should see the output from SCons simillar to this:
<screen>
user@host:$ scons po-update
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Writting 'messages.pot' (new file)
msginit --no-translator -l pl -i messages.pot -o pl.po
Created pl.po.
msginit --no-translator -l en -i messages.pot -o en.po
Created en.po.
msginit --no-translator -l de -i messages.pot -o de.po
Created de.po.
scons: done building targets.
</screen>
</para>
<para>
If everything is right, you shall see following new files.
<screen>
user@host:$ ls *.po*
de.po en.po messages.pot pl.po
</screen>
</para>
<para>
Open <filename>en.po</filename> in <command>poedit</command> and provide
english "translation" to message <literal>"Hello world\n"</literal>. Do the
same for <filename>de.po</filename> (deutsch) and
<filename>pl.po</filename> (polish). Let the translations be, for example:
<itemizedlist>
<listitem><para>
<literal>en: "Welcome to beautiful world!\n"</literal>
</para></listitem>
<listitem><para>
<literal>de: "Hallo Welt!\n"</literal>
</para></listitem>
<listitem><para>
<literal>pl: "Witaj swiecie!\n"</literal>
</para></listitem>
</itemizedlist>
</para>
<para>
Now compile the project by executing <command>scons</command> command. The
output should be similar to this:
<screen>
user@host:$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
msgfmt -c -o de.mo de.po
msgfmt -c -o en.mo en.po
gcc -o hello.o -c hello.c
gcc -o hello hello.o
Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
</screen>
SCons automatically compiled <literal>PO</literal> files to binary format
<literal>MO</literal>, and the <literal>InstallAs</literal> lines installed
these files under <filename>locale</filename> folder.
</para>
<para>
Your program should be now ready. You may try it as follows (linux):
<screen>
user@host:$ LANG=en_US.UTF-8 ./hello
Welcome to beautiful world
</screen>
<screen>
user@host:$ LANG=de_DE.UTF-8 ./hello
Hallo Welt
</screen>
<screen>
user@host:$ LANG=pl_PL.UTF-8 ./hello
Witaj swiecie
</screen>
</para>
<para>
To demonstrate further life of translation files, let's change polish
translation (<command>poedit pl.po</command>) to <literal>"Witaj drogi
swiecie\n"</literal>. Run <command>scons</command> to see how scons
reacts to this
<screen>
user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
</screen>
</para>
<para>
Now, open <filename>hello.c</filename> and add another one
<literal>printf</literal> line with new message.
<programlisting>
/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
bindtextdomain("hello", "locale");
setlocale(LC_ALL, "");
textdomain("hello");
printf(gettext("Hello world\n"));
printf(gettext("and good bye\n"));
return 0;
}
</programlisting>
</para>
<para>
Compile project with <command>scons</command>. This time, the
<command>msgmerge(1)</command> program is used by SCons to update
<literal>PO</literal> file. The output from compilation is like:
<screen>
user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Writting 'messages.pot' (messages in file were outdated)
msgmerge --update de.po messages.pot
... done.
msgfmt -c -o de.mo de.po
msgmerge --update en.po messages.pot
... done.
msgfmt -c -o en.mo en.po
gcc -o hello.o -c hello.c
gcc -o hello hello.o
Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
msgmerge --update pl.po messages.pot
... done.
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
</screen>
</para>
<para>
The next example demonstrates what happens, if we change the source code
in such way, that the internationalized messages do not change. The answer
is, that none of translation files (<literal>POT</literal>,
<literal>PO</literal>) is touched (i.e. no content changes, no
creation/modification time changed and so on). Let's append another one
instruction to the program (after the last printf), so its code becomes:
<programlisting>
/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
bindtextdomain("hello", "locale");
setlocale(LC_ALL, "");
textdomain("hello");
printf(gettext("Hello world\n"));
printf(gettext("and good bye\n"));
printf("----------------\n");
return a;
}
</programlisting>
Compile project. You'll see on your screen
<screen>
user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Not writting 'messages.pot' (messages in file found to be up-to-date)
gcc -o hello.o -c hello.c
gcc -o hello hello.o
scons: done building targets.
</screen>
As you see, the internationalized messages ditn't change, so the
<literal>POT</literal> and the rest of translation files have not
even been touched.
</para>
</section>
|